1. Field of the Invention
The invention relates to a structure of a battery. More specifically, the invention relates to a structure of a battery having flat terminals.
2. Description of the Related Art
In recent years, the importance of secondary batteries such as lithium ion battery and nickel hydrogen battery as on-board power sources for vehicles and power sources for personal computers and mobile terminals is increasing. In particular, lithium ion batteries, which are lightweight and can achieve high energy density, are used as on-board, high-output power sources for vehicles.
In batteries of this type, flat terminals are welded to the ends of the positive and negative electrode current collectors, which are not coated with active material, (for example, foil-type current collectors) as terminals for input and output of current. For example, Japanese Patent Application Publication No. 2002-117825 (JP-A-2002-117825) describes a method of producing a battery in which the peripheral portions of an electrode assembly (current collectors), which are not coated with an electrode active material, are stacked in layers and rod-like portions of the electrode terminals (flat terminals) are integrally welded to the stacked peripheral portions with the stacked peripheral portions compressed in their thickness direction. Other examples include JP-A-2002-231214, JP-A-11-204101, JP-A-2003-249423 and JP-A-8-185850.
In the above conventional art, however, the flat terminals must be pressed against the active material uncoated portions of the current collectors (current-collecting foils) of the electrode assembly during the welding process. Thus, the flat terminals may be deformed or bent by the pressure during the welding process and may damage the current collectors (current-collecting foils). Such damage to the current collector may adversely affect the performance and safety of the battery. Also, if the flat terminals are bent outward, when the electrode assembly is inserted into a battery case, the flat terminals may interfere with the battery case and may not be inserted into the case smoothly.